Is there an API method for reading To, From, Subject, Preheader by email message ID?

I want to use the Marketo API to display the content of an email message by providing the email ID. 

I can retrieve the HTML of the message easily, and display that, but I also want to display the values of To:, From:, Subject and Preheader, ex: fromName, fromEmail, subject, preHeader.

The only methods I see that have access to these is "Update Email Metadata", "Update Email Content", and "Create Email".

Is there an undocumented way to simply read those additional values, or something I'm missing?

The goal is to be able to provide a preview of the email body and the other information via a single preview link, rather than having to resort to sending test messages to people we need reviews and approvals from. The existing method of sending links to "view online" versions of the previews also excludes the other values that need review. 

Maybe there's a much easier solution?

Thanks!